Fomblin® and Krytox® Fluids for
Electron Microscopes

These two pump fluids, Fomblin and Krytox, manufactured by
Ausimont and DuPont respectively, while quite similar in properties, it
must be emphasized that they are not the same identical product. We
will leave it up to the manufacturers to make the case as to just how they
are different and to what degree one is "better" than the other.

To the best of our knowledge, and so far as we know, any diffusion pump that
has been operating with Fomblin in an electron microscope application, and
which has had the pump fluid replaced with Krytox, has continued to perform
in a way that was indistinguishable from when the system was first charged
with the Fomblin product. And the reverse of that is true as well, one can
apparently convert from Krytox back to the Fomblin situation without any
negative effects.

Advantages of the perfluorinated polyether fluids in column instruments:

While all diffusion pump fluids do have some low level of molecular species
in the microscope column, the perfluorinated polyether species do not get
polymerized in the presence of the ionizing radiation as is the case for
hydrocarbon pump fluids.

The end result of this advantage is that the column runs cleaner, longer and
whatever contamination in the column that might other wise be present is
present but at much lower levels. Putting it another way, microscope
downtime is greatly reduced since the column runs much cleaner for much
longer periods of time.

Another benefit is that these fluids are much more heat stable and tend to
break down much more slowly than the hydrocarbon based alternatives. Or
putting it another way, one has a need to change pump fluids far less
frequently.

One note of caution:

Do not attempt to convert your hydrocarbon charged system without first
consulting with the manufacturer of your instrument. For one thing, you
want to make sure that your diffusion pump is within the design
specifications of the perfluorinated polyether pump fluids. And secondly,
this would also mean that you would need to convert the mechanical pump(s)
pumping out the diffusion pump to pumps charged with perfluorinated
polyether fluid as well, and this generally means purchasing altogether new
mechanical pumps since it is generally not possible to clean a mechanical
pump well enough that it will work properly in that kind of a situation!

SPI purchases Krytox from DuPont and repackages some of it into smaller
bottles so that a customer can purchase in quantities more appropriate to
the size of their diffusion pump. However when that is done that way, SPI
can not call the product (legally) Krytox. So we therefore call it
SPI-Tox which is our way of making sure our customers know that the
product, purchased as SPI-Tox has been repackaged by SPI Supplies but
product labelled as Krytox is in the original package as packaged by DuPont.